RE: [PATCH v6 0/2] Add l2reflect measurement application

["Morten Brørup" <mb@smartsharesystems.com>]

> From: Henning Schild [mailto:henning.schild@siemens.com]
> Sent: Wednesday, 21 September 2022 14.59
> 
> Am Wed, 21 Sep 2022 14:22:07 +0200
> schrieb Morten Brørup <mb@smartsharesystems.com>:
> 
> > > From: Henning Schild [mailto:henning.schild@siemens.com]
> > > Sent: Wednesday, 21 September 2022 13.27
> > >
> > > Am Wed, 21 Sep 2022 11:43:13 +0200
> > > schrieb Morten Brørup <mb@smartsharesystems.com>:
> > >
> > > > > From: Felix Moessbauer [mailto:felix.moessbauer@siemens.com]
> > > > > Sent: Friday, 2 September 2022 10.46
> > > > >
> > > > > Dear DPDK community,
> > > > >
> > > > > this patch provides the l2reflect measurement tool
> > > > > which will be discussed in our 2022 DPDK Userspace Summit talk:
> > > > > "Using DPDK OVS for deterministic low latency communication"
> > > > >
> > > > > While the code still might need some polish, we believe it is
> > > > > a good starting point for discussions about low latency
> > > > > networking in DPDK.
> > > > >
> > > > > The tool can also be used in a CI environment to contineously
> > > > > measure latencies across the evolution of DPDK and Linux.
> > > > >
> > > > > Best regards,
> > > > > Felix Moessbauer
> > > > > Siemens AG
> > > >
> > > > Dear Felix and Henning,
> > > >
> > > > Great to meet you at the 2022 DPDK Userspace conference.
> > > >
> > > > Have you considered using the Configuration Testing Protocol
> > > > (CTP), described in chapter 8 of the Ethernet specification from
> > > > 1984 [1], instead of your own packet format and the Local
> > > > Experimental Ethertype?
> > >
> > > No we have not, first time i hear about that. First type we used
> > > must have been 0xaffe or 0xdead, would have to dig through version
> > > control.
> >
> > You seem to be using the correct EtherType for an experimental
> > protocol like this. I was not opposing to that.
> >
> > >
> > > > [1]: http://decnet.ipv7.net/docs/dundas/aa-k759b-tk.pdf
> > > >
> > > > The CTP an obsolete protocol, and not part of the IEEE standards
> > > > for Ethernet, but I think Wireshark is able to parse such
> > > > packets.
> > >
> > > Yes ... does not seem to be a train one wants to hop on.
> > >
> > > Maybe you can explain how one would use CTP to measure roundtrip
> > > times, and go into detail on how that would add value.
> >
> > I would only change the packet format, not the way of measuring.
> >
> > >
> > > I had a quick look at the spec and did not clearly see whether the
> > > protocol could be used at all ... maybe "abused". And being a CTP
> > > server one would need to implement more than just "reply". And i do
> > > not see any value, except maybe "wireshark support" ... but i am
> > > not sure how that would add value. The packets we send are trivial,
> > > headers are ethernet and the content does not matter ... so
> > > wireshark support is there for all relevant fields.
> >
> > The primary - and probably only - advantage would be that the
> > EtherType 0x9000 is officially allocated for CTP, so you don't need
> > to use one of the EtherTypes allocated for experimental purposes,
> > which might also be used for other purposes.
> 
> Yes that is something i thought about as well. In case there would be
> some sort of conflict with 88B5 i would rather include some sort of
> "magic start" or sub-protocol id if you want.
> But until we see such a conflict i would simply stick with 88B5 which
> seems to be a good fit, but not "clearly standardized". I would not
> envision people running l2reflect on a very busy/big network, as the
> results would become increasingly fuzzy and meaningless and other
> latency benchmarks would probably be a better fit.
> 
> Any confusion with another 88B5 application is "highly unlikely". And
> when jumping on 9000 we switch from one "unlikely number" to another
> one ... or in fact we are now on one that is "more likely"? From what i
> read cisco equipment might start acting on those 9000 packets.

Yes, 9000 are "more likely". Also good point about the Cisco risk.

> 
> I think a "highly unlikely" conflict does not justify a rewrite. For a
> not well defined protocol it would not be a "conflict" really. While
> 9000 would be "more likely" and dictate a corset to try and fit in.
> Even if we can make it fit today, future extensions might not work out.
> 
> So i think i would stay away from CTP.
> 
> Henning

Thanks for sharing your thoughts and analysis. I agree, then.

Series-Acked-by: Morten Brørup <mb@smartsharesystems.com>